Optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal. They are used in many industrial and consumer applications. As ambient light sensors (ALS) optical sensors are commonly used to automatically control the brightness of displays depending on the intensity of ambient light, both for user comfort, and for the purpose of conserving battery power in handheld devices.
An optical sensor should robustly respond to light striking a sensor aperture from a wide range of angles. At the same time, the range of angles or field of view should not be too wide as many optical sensors are prone to error when light incidents the sensor surface at large angles. A further source of error constitutes light that does not originate from ambient surroundings but rather comes from within the device itself, e.g. from stray light from a screen display, backlight in a mobile phone or from light emitted by neighboring active sensors. This leads to optical crosstalk and eventually reduction of signal to noise ratio.
Packaging technology aims at reducing the above-mentioned sources of error. Apertures in the sensor package define a range of limiting angles and reduce optical crosstalk from ambient surroundings and neighboring electronic components. Current open cavity package technologies, however, are either complex and therefore costly, or else cannot be used for most wafer-level applications because the requirements on aspect ratio and pin dimensions can be critical (or both).